Intermediates for the preparation of 1-(phenyl)-1-hydroxy-2-amino-3-fluoro propane derivatives

ABSTRACT

A process for preparing a compound of formula (I) ##STR1## wherein R is a methylthio, methylsulfoxy, methylsulfonyl or a nitro group; and 
     X4 is --OH, fluorine or --O--SO 2  R6 where R6 is methyl, trifluoromethyl, phenyl or p-methylphenyl which comprises contacting of a compound of formula (III) ##STR2## where R2 is C 1-4  alkyl; and R and X4 have the above mentioned meanings, with a strong base selected from the group consisting of alkali earth metal alcoholates, alkaline earth metal alcoholates, and tertiary amines in an aprotic solvent, to obtain the compound of formula (I).

This is a division of application Ser. No. 07/841,075, filed on Feb. 25,1992 now U.S. Pat. No. 5,243,056, which is a division of Appln. Ser. No.07/162,247, filed Feb. 29, 1988, now U.S. Pat. No. 5,105,009 which is acontinuation of Appln. Ser. No. 06/616,086, filed Jun. 1, 1984, nowabandoned.

This invention relates to new intermediates useful for preparing1-(phenyl)-1-hydroxy-2-amino-3-fluoro-propane derivatives.

More particularly this invention relates to new Compounds of Formula##STR3## where R is a methylthio, methylsulfoxy, methylsulfonyl or anitro group; and

X1 is hydrogen, 1-6 C alkyl, 1-6 C haloalkyl, 3-6 C cycloalkyl, phenylor phenylalkyl(1-6C), where the phenyl ring may be substituted by one ortwo halogen, 1-3 C alkyl, 1-3 C alkoxy or nitro; or

X1 together with X2 is an oxygen atom or an alkylene having from two tofive Carbon atoms; or

X1 together with X2 and R4 is a chain of formula ##STR4## where p is 3or 4 and q is 1 or 2; and X2 is hydrogen 1-6 C alkyl, 1-6 C haloalkyl,3-6 C cycloalkyl or phenyl which may be substituted by one or twohalogen, 1-3 C alkyl, 1-3 C alkoxy or nitro; or

X2 together with X1 has the above mentioned meanings; or

X2 together with R4 is ##STR5## where n is 1 or 2; m is 0 or 1; X ishydrogen, halogen, 1-3 C alkyl, 1-3 C alkoxy or nitro; or

X2 together with X1 and R4 has the above mentioned meanings; and

X3 is hydrogen or --CO--R4 where R4 is hydrogen, 1-6 alkyl, 1-6 Chaloalkyl, 3-6 C cycloalkyl, phenylalkyl(1-6C) or phenyl where thephenyl ring may be substituted by one or two halogen, 1-3 C alkyl, 1-3 Calkoxy or nitro; or

R4 together with X2 has the above mentioned meanings; or

R4 together with X2 and X1 has the above mentioned meanings; and

X4 is --OH, fluorine, OCOAlkyl(1-4C), -O-trialkyl(1-6 C)silyl,-O-tetrahydropyranyl, -O-tetrahydrofuranyl or --O--SO₂ R6 where R6 ismethyl, trifluoromethyl, phenyl or p-methyl-phenyl provided, however,that X4 is not OH when R is a nitro group.

which are useful as intermediates for preparing Compounds of Formula:##STR6## wherein R is --NO₂, CH₃ S--, CH₃ SO--, and CH₃ SO₂ ; and

R1 is mono-, di-, and tri-halomethyl.

The Compounds of Formula II contain two asymmetric carbon atoms and canexist as stereoisomers. Unless otherwise specified herein or in theclaims, it is intended that all four stereoisomers are included, whetherseparated or mixtures thereof. The D-(threo)-forms are preferred becauseof their broader antibacterial activity.

U.S. Pat. No. 4,235,892 discloses the Compounds of Formula II and aprocess for their preparation. This process essentially consist ofN-protecting a 1-(phenyl)-2-amino-1,3-propanediol, (the phenyl moiety ofwhich is variously substituted) by an imido derivative of a dicarboxylicacid, of treating the thus obtained compound withdialkylaminosulfotrifluoride (DAST), of removing the N-protecting groupand then of acylating the thus obtained1-(phenyl)-1-hydroxy-2-amino-3-fluoro-propane with the desiredhaloacetic acid or with a suitable reactive derivative thereof.

Although apparently easy, this process suffers many disadvantages andaffords low yields.

One of the main disadvantages is that the fluorination of the primaryhydroxy group is not selective and leads to the formation of manybyproducts, among which may be mentioned, for instance, the productsderiving from the substitution at the secondary hydroxy group. Thedesired compound may thus be obtained at a sufficient degree of purityonly by a particularly complex column chromatography process. Anotherdisadvantage is that DAST is the only agent which allows performance tothe fluorination step on the peculiar intermediate products which areprepared according to the process of U.S. Pat. No. 4,235,892 and DAST isvery expensive and dangerous, especially when it is intended for largescale production.

It has now been found that the above mentioned disadvantages can beovercome by using new Compounds of Formula I wherein either the aminogroup or the secondary hydroxy group of the 1-(phenyl)-2-amino1,3-propanediol derivative are protected.

Preferably also the primary hydroxy group is substituted by a leavinggroup which can be replaced by a fluorine atom.

The Compounds of Formula I have the advantage to avoiding the formationof many by-products and this not only in that the protection hinders thefluorination of the secondary hydroxy group but also in that it insuresthe stability of the configuration of the asymmetrc carbon atoms.

Furthermore the Compounds of Formula I are quite soluble in the mostpart of the aprotic organic solvents, thus allowing the fluorinationstep to be carried out also in homogeneous phase and under anhydrous andmild conditions.

Another advantage is that the Compounds of Formula I are prepared veryeasily by making use of cheap reactants and that the protective groupscan be removed very easily as well after the completion of thefluorination step.

Still another advantage of the Compounds of Formula I is that theprotection of the secondary hydroxy group allows the substitution of theprimary hydroxy group with a suitable leaving group so that thefluorination step can be most conveniently carried out with fluorinationagents which are cheaper and less dangerous than DAST.

The protection of the amino and of the secondary hydroxy group thusperformed is substantially inert to those treatments that the moleculeundergoes, more particularly with nucleophiles and bases, up to thefluorination step and can then be easily removed under mild conditions.

When X1, X2 and R4, independently represent hydrogen, 1-6 C alkyl, 1-6 Chaloalkyl, 3-6 C cycloalkyl, phenyl or substituted phenyl, examples ofsuitable reactants are:

aldehydes such as formaldehyde, acetaldehyde,α,α,β-trichlorobutyraldehyde, cyclohexanecarbaldehyde, valeraldehyde,caproaldehyde, benzaldehyde, p-methylbenzaldehyde, anisaldehyde,4-chlorobenzaldehyde, 4-ethoxy-3-methoxy-benzaldehyde,2,6-dinitrobenzaldehyde or ketones such as acetone diethylketone orhexylmethylketone for protecting the secondary hydroxy group and onehydrogen of the amino group, and

acids such as acetic, dichloroacetic, trifluoroacetic, pivaloyl,benzoic, cyclohexanecarboxylic 2,4-dibromobenzoic, veratric,2,5-dimethylbenzoic, phenylacetic or 4-nitrobenzoic acid, for protectingthe second hydrogen of the amino group.

When X1 and X2, together, are an alkylene radical having from 2 to 5carbon atoms, examples of suitable reactants are the cycloalkanones suchas cyclopropanone, cyclopentanone or cyclohexanone.

When X1 together with X2 and R4 is a chain of formula ##STR7## where pand q have the above mentioned meanings, examples of suitable reactantsare the ketoacids such as (2-oxocyclopentyl) aceticacid,(2-oxocyclohexyl)-acetic acid, 3-(2-oxocyclopentyl) propionic acidand 3-(2-oxocyclohexyl)-propionic acid.

When X2 together with R4 forms a mono- or a poly-cylic system, examplesof suitable reactants are the aldehydo-acids or the keto-acids such asphthalaldehydic acid, succinic semi-aldehyde, levulinic acid,4-phenyl-4-oxo-butyric acid; hexahydrophthalaldehydic acid;(2-acetyl)-cyclohexylcarboxylic acid and(2-acetyl)-cyclopentyl-carboxylic acid.

When X1 together with X2 is an oxygen atom, examples of suitablereactants are the halocarbonates of formula XCOOR₂ where X is a halogenatom and R2 is an alkyl, aralkyl or an aryl radical; preferably R2 is an1-4 C alkyl radical.

The methods for preparing the Compounds of Formula I change according tothe nature of the desired Compound. Excepting those where X1 and X2together are an oxygen atom, they can be prepared according to knowntechniques.

The preparation of Compounds I where X1 and X2, together, are an oxygenatom is based on the unexpected finding that compounds of Formula##STR8## where R, X4 and R2 have the above mentioned meanings, cyclizeregioselectively on the secondary hydroxy group to afford oxazolidinonesof Formula I, in the presence of strong bases and of aprotic solvents.

The role of the solvent is critical. When the reaction is carried out inthe presence of a non-aprotic solvent, the cyclization proceeds eitheron the secondary or on the primary hydroxy group and affords a mixtureof the two possible cyclic compounds.

Examples of suitable aprotic solvents are the aromatic hydrocarbons suchas benzene and toluene. Examples of suitable strong bases are the alkaliand the alkaline earth metal alcoholates as well as the tertiary amines.

The cyclization reaction may also proceed via the intermediate formationof the alcoholate at the secondary hydroxy group when they are usedalkali and alkaline earth metal alcoholates, alkali metal hydrides suchas sodium hydride, sodium amide, Grignard-like organo-metallicderivatives and alkyl-lithium derivatives.

In their turn, the compounds (III)can be prepared according to knowntechniques such as the reaction of the desired1-(phenyl)-2-amino-1,3-propanediol, substituted at the phenyl ring, witha compound of formula X--COOR2, where X is halogen and R2 has the abovementioned meanings, in the presence of a base and of a suitable diluent.

When an organic diluent is used such as acetonitrile, there ispreferably used an organic base such as a tertiary amine whereas aninorganic base such as an alkali metal carbonate or bicarbonate, ispreferably used when the reaction is carried out in aqueous medium.Alternatively a basic diluent such as pyridine may be used.

The compounds of formula III wherein R is --SCH₃ are more soluble in theaprotic solvents, than those wherein R is --SO--CH₃ or SO₂ CH₃. Apreferred way for preparing Compounds (I) wherein R is --SO--CH₃ or--SO--CH₃ comprises the preparation of the corresponding Compounds(III)wherein R is --S--CH₃, their subsequent cyclization and lastly, theiroxidation according to known techniques.

The substitution of the hydrogen of the primary hydroxy group with aCOAlkyl(1-4C) trialkyl(1-6C)-silyl, tetrahydropyranil, tetrahydrofuranyland a --SO₂ R6 radical, where R6 has the above mentioned meanings, canbe carried out before or after the protection of both the secondaryhydroxy and amino group. Also this substitution can be carried outaccording to known techniques.

The fluorination of Compounds I where X4 is not fluorine can be carriedout either with DAST or with less expensive and more amenablefluorination agents such as FAR(1-diethylamino-1,1-di-fluoro-2-chloro-2-fluoro-ethane), phosphorusfluorides, hydrofluoric acid optionally as a salt with soluble orpolymeric tertiary amines and, alkali and alkaline-earth metalfluorides.

Examples of suitable fluorination agents when X4 is --OH are FAR,phosphorus fluorides and hydrofluoric acid.

When FAR is used, the reaction is carried out under anhydrous conditionsand in homogeneous phase, preferably in acetonitrile at the boilingtemperature.

After performance of the fluorination step, the protective groups areremoved from the Compounds of Formula I wherein X4 is fluorine.

A preferred method consists of removing the protective groups withacids, preferably inorganic acids, in aqueous medium or in water/organicdiluents mixtures. The latter media are preferred when hydrolysisregenerates the compound or the compounds which had been previously usedas protective agents and when the amine which is formed is soluble in anaqueous solution of inorganic acids. There is thus obtained a partitionof the amine in the aqueous layer and of the protective agent or agentsin the organic layer, from which they are recovered and then recycled;in its turn, the amine is recovered by precipitation via neutralizationof the aqueous layer. Alternatively the amine can be extracted with asuitable organic solvent.

When X1 and X2, together are an oxygen atom, the protective group mayalso be removed through treatment with an organo-metallic derivativesuch as a Grignard's derivative and the subsequent hydrolysis in mildconditions with inorganic acids in water or in water/organic solventmixtures.

Another possible method for removing the protective group when X1 andX2, together, are an oxygen atom, comprises the reduction of the ketogroup and the subsequent hydrolysis in mild conditions as describedabove. This reduction is preferably carried out with complex hydridessuch as sodium borohydride.

After removal of the protective groups there is obtained a compound ofFormula ##STR9## which can be reacted with a haloacetic acid of FormulaR1COOH, wherein R1 has the above mentioned meanings, or a reactivederivative thereof to afford the desired compound of Formula (II).

The protection performed by the Compounds of Formula I is useful notonly for preparing the compounds of Formula II, but also whenever it isdesired to replace the primary hydroxy group with another functionalgroup, such as chlorine, bromine, iodine, nitrile, hydrogen, --OR₇,--SR₇, --SCOR₇, --SCN, --S(═NH)NH₂, --CH--(COOR₇)₂, wherein R7 is alkyl,aralkyl or aryl.

This invention is illustrated by the following examples which should notbe constructed as limiting it in any way.

EXAMPLE 1 Preparation of3-acetoxy-1-(4-methylsulfonyl-phenyl)-2-phthalimido-1-hydroxy-propane(A)

D-(threo)-1-(p-methylsulfonylphenyl)-2-phthalimido-1,3-propanediol (1 g;2.66 mmols), prepared as described in U.S. Pat. No. 4,235,892, has beendissolved in anhydrous pyridine (5 ml). Acetylchloride (0.2 ml; 2.83mmols) has been added dropwise to this solution kept under stirring at0° C.; after completion of the addition, the reaction mixture has beenheated to 25° C. and kept under stirring for 1 hour; afterwards, thereaction mixture has been poured into water and ice, acidified withhydrochloric acid and extracted with ethyl acetate.

The crude product (A) has been obtained (quantitative yield) from theorganic layer after drying over sodium sulfate and evaporation of thesolvent in vacuo; the crude, after crystallization from methanol, gave apure product (0.84 g; yield 75%) as shown by HPLC and TLC analysis.

Elemental Analysis for C₂₀ H₁₉ O₉ N (found) C 57.3% ; H 4.6% ; N 3.3%(Calculated) C 57.55%; H 4.56%; N 3.36%.

The acetylation is regio-selective on the secondary hydroxy group asshown by NMR spectrum in DMSO; delta=1.78; s, 3H, CH₃ CO--; 4.50 dd- 2H,--CH₂ OAc; 6.02,d,1H, benzylic OH.

EXAMPLE 2 Reduction of Compound (A) to3-acetoxy-1-(4-methylsulfonyl-phenyl)-hydroxy-2-(3-hydroxy-1H-isoindol-1-one-2-yl)-propane(B)

Compound (A) (0.76 g; 1.82 mmols) has been added to a mixture oftetrahydrofuran and water (1:1; 4 ml); to this suspension, kept at 0° C.under vigorous stirring, has been added portionwise sodium borohydride(138 mg; 3.64 mmols).

As the reaction proceeded, the suspension became a homogeneous solution,after 1 hour and after having checked by TLC the disappearance ofcompound (A) and the formation of a new product, tetrahydrofuran hasbeen evaporated in vacuo and the product extracted with ethyl acetate.

After drying over sodium sulfate and evaporation of the solvent,compound (B) (0.7 g; yield 92%) has been obtained sufficiently pure toundergo as such the following reaction (Example 3).

Compound (B) proved to be a mixture of two diasteroisomers because ofthe formation, during the reduction step, of a new asymmetric carbonatom; this has been proved by TLC, HPLC and NMR spectra in DMSOcontaining D₂ O; delta 1.78; s, and 1.86, s, 3H on the whole, CH₃ --COin two diastereoisomers in the ratio 35:65; 5.84,s, and 6.24,s,1H, onthe whole ##STR10## of the isoindole system (doublets, beforedeuteration, coupled with two doublets ehibiting delta=6.8 and 6.57respectively, 1H on the whole for --OH in the two diastereoisomers) and,finally, 5.14, d, and 5.2, d, 1H on the whole for the two ##STR11## inposition 1 of the propane chain.

EXAMPLE 3 Cyclization of Compound (B) to3-acetoxymethyl-2-(4-methyl-sulfonyl-phenyl)-2,3-dihydro-oxazole-2,3,a!-isoindol-5(9bH)-one (C)

Product (B) (0.55 g; 1.3 mmol) has been suspended in benzene (5 ml)containing a little amount of p-toluensulfonic acid (5 mg); by heating,the mixture became a clear solution. A short time later the water formedduring the reaction has been distilled azeotropically until water wasabsent in the distilled benzene and TLC analysis showed thedisappearance of product (B). At the end, almost all benzene has beenevaporated in vacuo; after having added some water, product (C) has beenextracted with ethyl acetate. Crude product (C) has been obtained inquantitative yield from the organic phase after drying over sodiumsulfate and evaporation of the solvent in vacuo.

Crude product (C) has been used as such for the subsequent hydrolysis(Example 4). An aliquot has been purified by chromatography on silicagel using ethyl acetate/petroleum ether in various ratios or pure ethylacetate as eluants. It has been proved that the crude contained smallamounts of some unidentified impurities; after purification bychromatography has been proved to be a mixture of two diasteroisomers asshown by TLC and HPLC analysis as well as by NMR spectrum in DMSO: delta6.38,s, and 6.07 s, 1H on the whole, ##STR12## of the isoindole system;2.08 s and 2.18 s, 3H on the whole, CH₃ CO--; 3.19, s and 3.24, s, 3H onthe whole, CH₃ SO₂ --.

Elemental analysis for C₂₀ H₁₉ O₈ N (calculated): C, 59.85%; H, 4.74%;N, 3.49% (found) C, 59.9% ; H, 4.6% ; N, 3.6%

EXAMPLE 4 Hydrolysis of Compound (C) to2-(4-methylsulfonyl-phenyl)-3-hydroxymethyl-2,3-dihydro-oxazole-2,3,a!-isoindol-5(9bH)-one (D)

Product (C) (0.2 g; 0.5 mmols) has been dissolved in methanol (2 ml)containing potassium hydroxide (42 mg; 0.75 mmols) at 0° C. and undervigorous stirring. After 30' the hydrolysis has been checked by TLC andshowed the disappearance of product (C).

Methanol has been evaporated in vacuo and in the cold; the residue hasbeen treated with water and extracted with ethyl acetate. The organiclayer has been dried and evaporated to afford product (0) which has beenrecrystallized from ethyl acetate (0.16 g; yield 89%). The presence oftwo diastereoisomers in product (D) has been shown by NMR spectrum inDMSO, delta=6.3, s and 5.82,s, 1H on the whole, ##STR13## of theisoindole system; 3.18,s, and 3.22,s, 3H on the whole, CH₃ SO₂ --.

EXAMPLE 5 Preparation of2-(4-methylsulfonyl-phenyl)-3-fluoromethyl-2,3-dihydroxazole-2,3,a!-isoindol-(9bH)-one (E)

35 ml of anhydrous acetonitrile, cooled to 0° C., has been added with3.2 ml (20 mmols) of FAR(1-diethylamino-1-difluoro-2-chloro-2-fluoroethane). After 10 minutescarefully dried compound (D) (5 g; 13.9 mmols) has been addedportionwise; when the addition has been over, the solution has beenrefluxed for 2 hours. After completion of the reaction, the solvent hasbeen evaporated in vacuo and the residue, after treatment with water andice, has been extracted with ethyl acetate. The organic layer has beendried over sodium sulfate and evaporated in vacuo to afford crude (E),which has been used as such for the subsequent hydrolysis (Example 6);an aliquot has been purified by chromatography on silica gel and thediastereoisomer present in the mixture in largest amount has beenisolated and showed a very high purity degree.

NMR spectrum in CHCl₃ : delta=3.04,s,3H, CH₃ SO₂ : 4.18,m,1H, ##STR14##5.58, d, 1H, J=6 cps, H--C--O--; 6.20, s,1H, ##STR15## 4.82, m, 2H,J_(H).sbsb.1_(F) =48 Hz.

EXAMPLE 6 Hydrolysis of Compound (E) and Preparation ofD-threo-1-(4-methylsulfonyl-phenyl)-1-hydroxy-2-dichloroacetamido-3-fluoro-propane(F)

Compound (E) (2.07 g; 5.73 mmols) has been suspended in 2N HCl (60 ml)and the suspension refluxed for 7 hours.

After cooling, the mixture has been extracted with ethyl ether torecover the phthalaldehydic acid formed during the hydrolysis step.

The aqueous layer has been saturated with sodium chloride and potassiumcarbonate, extracted with ethyl acetate and then with chloroform.

The combined organic extracts has been dried over sodium sulfate andevaporated in vacuo. The crude product thus obtained, which, withoutfurther purification, has been treated, at the boiling temperature for 6hours, with methyl dichloroacetate (6 ml) in the presence of catalyticamounts of triethylamine. After completion of the reaction, the volatilecompounds has been removed and the residue has been chromatographed onsilica gel while collecting the fractions containing (F). Compound (F)has been compared with a sample obtained according to another process(U.S. Pat. No. 4,235,892) and proved, by analytical and microbiologicaltests, to be identical with the sample.

EXAMPLE 7 Preparation of2-(4-methylsulfonyl-phenyl)-3-methansulfonyl-oxymethyl-2,3-dihydro-oxazole2,3,a!-isoindol-5-(9bH)-one (G)

Freshly distilled methanesulfonyl chloride (0.35 ml; 4.59 mmols) hasbeen added to a solution of compound (D) (1.5 g; 4.17 mmols) in pyridine(3 ml), kept at 0° C. and under stirring. The mixture was allowed tostand in refrigerator overnight and then added with ice and extractedwith ethyl acetate. The combined organic extracts has been dried oversodium sulfate and the solvent removed by evaporation.

Compound (G) has been thus obtained in a purity degree sufficient toundergo the subsequent reaction (Example 8).

EXAMPLE 8 Preparation of Compound (E) from (G)

Compound (G) (1.48 g; 3.38 mmols) has been dissolved in warm toluene (7ml). This solution was added with an aqueous solution of potassiumfluoride (4 ml; solution consisting of 3 g of potassium fluoride and 3 gof water) and with hexadecyltributylphosphonium chloride (0.28 g).

The thus obtained heterogeneous mixture has been refluxed under vigorousstirring for 7 hours. The organic layer has been then separated andevaporated; the residue has been treated with water and extracted withethyl acetate. The organic layer has been dried over sodium sulfate andevaporated to afford crude product (E) which has been purified bychromatography on silica gel. The thus obtained product showed the samecharacteristics as the product obtained according to Example 5.

EXAMPLE 9 Preparation of1,3-dihydroxy-1-(4-methylthio-phenyl)-2-ethoxycarbonylamino-propane (H)

D-(threo)-1-(4-methylthio-phenyl)-2-amino-1,3-propanediol (1.06 g; 4.93mmols) has been suspended into an aqueous solution of potassiumcarbonate (1.8 g of potassium carbonate into 20 ml of water) and thethus obtained mixture has been cooled, under vigorous stirring, to 0° C.

Ethyl chlorocarbonate (0.5 ml) has been dropped quickly into the mixturemaintained under vigorous stirring at 0° C.; after half a hour, further0.24 ml of ethyl chlorocarbonate (total amount: 7.74 mmols) has beenadded and the mixture has been maintained under stirring for 1 furtherhour.

At first the reaction mixture became clear and then a white precipitatehas been slowly formed. After having checked the completion of thereaction by TLC, the suspension has been extracted with ethyl acetate.After drying on sodium sulfate, filtration and evaporation of thesolvent, the organic extracts afforded 1.37 g of crude (H) (yield,95.5%) which has been recrystallized from ethyl acetate/diisopropylether. m.p.=75° C.

I.R. spectrum: 3340 and 3450 cm⁻¹ (OH, NH stretching), 1690-1700 cm⁻¹(broad band: C=0 amide).

In a similar manner there has been prepared the1,3-dihydroxy-1-(4-methylsulfonyl)-phenyl-2-ethoxycarbonylamino-propane(I) which, after crystallization from ethyl acetate, showed (IRanalysis) the following peaks: 3200-3360 cm⁻¹ (broad band--OH and NHstretching), 1715 cm⁻¹ (CO amide).

EXAMPLE 10 Cyclization of Compound (H) to5-(4-methylthio-phenyl)-4-hydroxy-oxazolidin-2-one (J)

Compound (H) (5 g; 17.5 mmols) has been dissolved in warm toluene (25ml). To this solution, an equimolar amount of potassium tert butylatehas been added and the reaction mixture has been refluxed for 3 hours.Afterwards, almost all of the solvent has been evaporated; water and icehave been added to the residue and the precipitate has beeen collectedby filtration. The thus obtained crude (J) has been recrystallized fromethanol (3.7 g; yield, 88%); m.p. 130-131° C.

I.R. Spectrum: 3180, 3240, 3300 cm⁻¹ (OH an NH stretching) 1720; 1745cm⁻¹ (C=0, oxazolidinone); NMR in DMSO, delta: 7,64 and 8,0, twodoublets, 2H each one of p-substituted phenyl; 7.88, S, 1H, NH amido;5.48, d, 1H, benzyl hydrogen; 3.56, m, 2H, hydroxymethyl; 5.16, m, Hlinked to C4 of oxazolidinone ring; 3.2, S, 3H, CH₃ S--.

EXAMPLE 11 Oxidation of Compound (J) to5-(4-methylsulfonyl-phenyl)-4-hydroxymethyl-oxazolidin-2-one (K)

Compound (J) (53 g; 221 mmols) has been added portionwise to 84 ml ofhydrogen peroxide (130 vol.) maintained under stirring at 40-45° C.After completion of the addition, the stirring has been continued forfurther 20 hours at 40° C.

Acetic anhydride (76.6 g; 20.7 ml) has been dropped into the reactionmixture by keeping the temperature below 40° C.

The reaction mixture has been then cooled to 20-22° C. and maintainedunder stirring at this temperature for 3 hours and, finally, allowed tostand in refrigerator overnight.

Afterwards, the solvent has been evaporated with caution in vacuo at 40°C.; hot ethanol has been added to the thus obtained residue. The solventhas been again evaporated and the residue crystallized from methylalcohol. 48.6 g of product (K) yield, 81%. m.p. 172-174° C.

I.R. spectrum: 1710 cm⁻¹ (C=0, amide) 3470, 3340, 3250, 3200 cm⁻¹ (OHand NH).

EXAMPLE 12 Preparation of5-(4-methylsulfonyl-phenyl)-4-fluoromethyl-oxazolidin-2-one (L) from (K)

To 1 ml of acetonitrile at 0° C. have been added two drops of FAR and,after some time, anhydrous compound (K) (100 mg; 0.42 mmols);afterwards, has been added the remaining aliquot of FAR (total amount:1.5 mols to each mole of compound K); the suspension has been maintainedunder stirring at 0° C. for 10 minutes and the temperature has been thenallowed to rise up to 20° C. When the suspension became clear it, hasbeen refluxed for 3 hours. After evaporation of the solvent, the residuehas been treated with water and ethyl acetate. The organic extract hasbeen dried over sodium sulfate, evaporated to dryness and the residue(90 mg) chromatographed on silica gel. Pure product (L) has been thusobtained (45 mg).

I.R. spectrum: 1750 cm⁻¹ (C=0, oxazolidinone) N.M.R. in DMSO, delta:7.70 and 8.05, two doublets, 2H each one of 4-substituted phenyl; 8.16,S, NH amido; 5.6, d, 1H, benzyl hydrogen; 4.74 and 4.5, two multiplets,1H each.

EXAMPLE 13 Preparation of5-(4-methylsulfonyl-phenyl)-4-methanesulfonyloxy-methyl-oxazolidin-2-one(M) from (K)

Compound (K) (200 mg; 0.84 mmols) has been dissolved in anhydrouspyridine (3 ml). The thus obtained solution has been cooled to 0° C. andadded with freshly distilled methanesulfonyl chloride (0.06 ml). Thesolution has been maintained at 0° C. overnight and then diluted with anaqueous solution of hydrochloric acid (stoichiometric amount withrespect to pyridine) and ice. After extraction with ethyl acetate, theorganic extract has been dried over sodium sulfate and evaporated invacuo to afford crude (M); yield, 85-90%.

I.R. spectrum: 3300 cm⁻¹ (NH), 1760 and 1740 cm⁻¹.

EXAMPLE 14 Preparation of (L) from (M)

Product (M) (155 mg; 0.44 mmols) has been suspended into 0.5 ml oftoluene; to this solution have been added hexadecyltributylphosphoniumbromide (22.3 mg) and a concentrate solution of KF (207 mg; 2.2 mmols)in water.

The reaction mixture has been refluxed under vigorous stirring for 6hours and then diluted with water. The aqueous layer has been extractedwith ethyl acetate; the combined organic extracts have been dried oversodium sulfate, evaporated in vacuo and the crude residue (110 mg) hasbeen chromatographed on silica gel to afford 40 mg of pure product (L).

We claim:
 1. A process for preparing a compound of formula (I) ##STR16##wherein R is a methylthio, methylsulfoxy, methylsulfonyl or a nitrogroup; andX4 is --OH, fluorine or --O--SO₂ R6 where R6 is methyl,trifluoromethyl, phenyl or p-methylphenyl which comprises contacting ofa compound of formula (III) ##STR17## where R2 is C₁₋₄ alkyl; and R andX4 have the above mentioned meanings, with a strong base selected fromthe group consisting of alkali earth metal alcoholates, alkaline earthmetal alcoholates, and tertiary amines in an aprotic solvent, to obtainthe compound of formula (I).
 2. A process according to claim 1, whereinthe alkali metal alcoholate is potassium tert butylate.
 3. A processaccording to claim 1, wherein the aprotic solvent is an aromatichydrocarbon.
 4. A process according to claim 3, wherein the aromatichydrocarbon is benzene or toluene.